In the semiconductor industry, silicon-on-insulator substrates may be formed using a process referred to in the art as separation by ion implantation of oxygen (SIMOX). In a SIMOX process, a Si wafer is implanted with oxygen at high doses (on the order of 5E16 atoms/cm2 or greater) and then annealed and oxidized at very high temperatures (on the order of about 1300° C. or greater) to form a well-defined and continuous buried oxide layer below the surface of the Si wafer. The high-temperature anneal serves both to chemically form the buried oxide layer as well as to annihilate any defects that persist in the near-surface silicon layer by annealing near the melting point of silicon.
Because of the recent high-level of activity using strained Si-based heterostructures, there is a need for providing SiGe-on-insulator (SGOI) substrates in which the SiGe layer is substantially relaxed and of high-quality. SGOI substrates may be formed using various processes including, for example, the SIMOX process. In the prior art, a thick SiGe layer having a thickness of about 1 to about 5 micrometers is first deposited atop a Si wafer and then the SIMOX process is performed. Such a prior art process suffers the following two drawbacks: 1) the Ge tends to diffuse into the bulk before a continuous oxide layer is formed and 2) the presence of Ge near the O peak inhibits the formation of a high-quality buried oxide layer unless the Ge concentration is very low.
In view of the drawbacks with prior art SIMOX processes of forming a SGOI substrate material, there is a need for providing a new and improved SIMOX method that reduces the tendency of Ge to diffuse into bulk Si before a continuous buried insulating layer is formed and provides a relaxed, high-quality SiGe alloy layer atop a buried insulating layer.